A novel poly(ethyleneimine)/Au nanoparticles/hemin nanocomposite (PEI-AuNPs-Hemin)acting for Methyl Orange (MO) removal has been synthesized.PEI-AuNPs was prepared firstly and it was then linked to hemin through the coupling between carboxyl groups in hemin and amino groups in PEI without the activation of carboxyl groups.The high reactivity and stability of AuNPs contributed greatly in the formation of the amido bonds in the nanocomposite.Fourier transform infrared spectroscopy,transmission electron microscopy and UV-visible spectroscopy were used to characterize the PEI-AuNPs-Hemin.Results show that PEI-AuNPs-Hemin has strong adsorption for MO.Adsorption and degradation experiments were carried out at different pHs,nanocomposite concentrations and UV irradiation times.Removal of MO in acidic solutions was more effective than in basic solutions.The real-time study showed that the MO degradation with the nanocomposite under UV irradiation was a fast process.In addition,the photocatalytic degradation mechanism was proposed.The study suggests that the PEI-AuNPs-Hemin may have promising applications in environmental monitoring and protection.(c) 2016 The Research Center for Eco-Environmental Sciences,Chinese Academy of Sciences.